Up-concentration of sugars in pretreated-rice straw by an osmotic pressure-driven method

Forward osmosis (FO), driven by high osmotic pressure, was used for the first time for bioethanol production from lignocellulosic biomass. A commercial membrane, TFC-ES (Hydration Technology Innovation), was used and 3.6 M triethylamine (TEA) was chosen as the draw solution because the concentration ratio against a model xylose solution was similar to that achieved with 2.5 M NaCl. The liquid fraction of hot-water-pretreated rice straw was concentrated by using the FO membrane. The initial sugar concentration of 199 mM increased to 825 and 1612 mM after 48 and 72 h of FO concentration, respectively, and these values were much higher than those obtained from nanofiltration. Simultaneous saccharification and fermentation of the liquid fraction after 48 h of FO concentration by xylose-fermenting recombinant Saccharomyces cerevisiae produced 17.7 g/L of ethanol after 24 h fermentation. Thus, the FO process has tremendous potential to up-concentrate sugars obtained from lignocellulosic biomass.